Musical Symbol Common Time

Each bar has four quarter-note beats.

That is the 4/4 reading: each beat is one quarter note. The sign sets the meter; the tempo tells how quickly to play it.

Why does the common-time sign look like C?

Its curve comes from a medieval semicircle sign.

In the fourteenth century, mensural notation—a system for writing rhythm—a breve (a long note) could divide into three shorter note values (“perfect”) or two (“imperfect”). A full circle marked the three-part division and a semicircle the two-part division. The older sign system gave way to modern meter notation about 1600 to 1700; the semicircle survived as common-time shorthand, not as an initial for “common.”